This invention relates generally to gas turbine engines and, more particularly, to a method and apparatus for minimizing the radial clearance between the rotor and shroud by automatically, and selectively, varying the position of the shroud in response to certain predetermined engine operating conditions.
As turbine engines continue to become more reliable and efficient by changes in methods, designs and materials, losses which occur from excessive clearances between relatively rotating parts become more important in the many design considerations. In many turbine engine applications, there is a requirement to operate at variable steady-state speeds and to transit between those speeds as desired in the regular course of operation. For example, in a jet engine of the type used to power aircraft, it is necessary that the operator be able to transit to a desired speed whenever he chooses. The resulting temperature and rotor speed changes bring about attendant relative growth between the rotor and the surrounding shroud and, in order to maintain the desired efficiency, this relative growth must be accommodated for. The primary concern is to maintain a minimum clearance between the stator and rotor while preventing any frictional interference therebetween which would cause rubbing and resultant increase in radial clearance during subsequent operation. When considering the transient operating requirements as mentioned hereinabove, the relative mechanical and thermal growth patterns of the rotor and shroud present a very difficult problem.
Various schemes have been devised to variably position the stationary shroud in response to engine operating parameters in order to reduce rotor/shroud clearance. One such apparatus which is shown and claimed in U.S. Pat. No. 3,966,354, issued on June 29, 1976 and assigned to the assignee of the present invention, regulates the amount of cooling air which flows over the turbine shroud support in response to the temperature of that cooling air. Other schemes for performing similar functions are shown in U.S. patent application Ser. No. 710,872, filed on Aug. 2, 1976 and assigned to the assignee of the present invention.
It is therefore an object of the present invention to provide an efficient turbine engine which is capable of transiting between various speeds while maintaining a minimum clearance between its rotor and shroud.
Another object of the present invention is the provision in a turbine engine for the selective modulation of the shroud position so as to minimize the clearance between the shroud of the rotor during operation under variable conditions.
Yet another object of the present invention is to selectively modulate the position of a rotor shroud in response to variable steady-state and transient operating conditions.
Still another object of the present invention is to automatically provide positive and variable positioning of a shroud with respect to a circumscribed rotor in order to maintain a minimum clearance therebetween during variable operating conditions.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.